The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention relates to a method for reducing the detonation potential of explosives manufactured from commercially available sources of inorganic oxidizing salts, such as commercial fertilizers.
2. Description of the Background
It is generally known that explosive devices can be manufactured from commercial grade fertilizers. For example, the explosive ANFO is a stoichiometrically balanced mixture of approximately 94% ammonium nitrate and 6% fuel oil or kerosene. ANFO is a high order explosive capable of detonation in response to a shockwave that passes through a block of the high explosive material. The shockwave breaks apart the molecular bonds between the atoms of the substance leaving mostly explosive gasses.
There are more than 800 different commercially available ANFO preparations. One of the more common mixtures uses xe2x80x9cprillsxe2x80x9d or pellets of ammonium nitrate mixed with diesel fuel to form a semi-liquid substance. A petroleum based oil such as kerosene fuel oils, lubricating oils or crude oil, or nitro-methane is sprayed onto the prilled ammonium nitrate in a mixer. The porous cavities of the prills absorb the fuel oil. Crosslinkers and pH buffers may be added and the mixture is blended to yield a uniform composition.
Some 95% of all commercial explosives work done in the U.S. for mining and commercial blasting uses specially prepared mixtures of ANFO. Commercially prepared ANFO is ideal not only for its destructive potential but also for its relative safety. It performs comparably to ammonium dynamite, but is so stable that spontaneous explosion is unlikely, and the material can be safely manufactured, stored, transported, and used.
To explode the ANFO, commercial explosive experts use a device called a detonator, containing a small amount of a highly explosive material, and a powerful booster charge that will create enough of a shock wave to set off the compound. A special type of detonator called a blasting cap is most frequently used. Common boosters include dynamite, water gel explosives, Dupont Corporation""s Detaprime cast boosters, and Atlas Powder Company""s Power Prime cast explosive.
Unfortunately, the widespread availability of ammonium nitrate has encouraged illicit production of ANFO for terrorist activity. For example, the bomb that destroyed the Alfred P. Murrah Federal Building in Oklahoma City on Apr. 19, 1995, the most destructive act of terrorism ever on American soil, was an ANFO explosive device. The attack of the USS Cole naval destroyer on Oct. 12, 2000 in the port of Aden, Yemen is supposed to have been carried out with an ANFO explosive device. Ammonium nitrate is widely available in the United States which produces an estimated 14 billion pounds of fertilizer grade ammonium nitrate each year. As long as detonable ammonium nitrate is readily available, the threat of terrorist misuse of the explosive will persist. Fertilizer grade ammonium nitrate is not as pure a preparation as the specially prepared ANFO for commercial blasting. Commercial fertilizer products do not work as well as porous ammonium nitrate prills, because fertilizers are coated with anti-caking agents, additives, and various materials meant to seal them from moisture, which keep the oil from being absorbed. However, information is available in books and on the Internet teaching treatments to convert commercial fertilizer to a functional starting material for an ANFO explosive device.
In the past, a variety of additives have been proposed which would desensitize ammonium nitrate formulations to detonation or severely curtail their explosive performance. However, many additives that have worked well in small scale tests either did not work well in large scale tests, were easily separated, or were environmentally hazardous. For example, water is known to be an ANFO desensitizer when it is present at a concentration of approximately 10% by weight. However, it is a simple matter for terrorists to dry the ammonium nitrate prior to mixing it with fuel oil.
Other efforts to desensitize ammonium nitrate have been directed to the explosive potential of the compound itself rather than ANFO. For example, U.S. Pat. No. 4,124,368 to Boyars discloses a method for reducing the accidental detonation of commercially produced mass quantities of ammonium nitrate by substituting up to 50% by weight of a solid solution of potassium nitrate in form III ammonium nitrate. The concentration of potassium nitrate reduces the probability of adverse phase changes in the ammonium nitrate, and consequently reduces the danger of explosion. Unfortunately, the concentration of potassium nitrate alters the composition of the fertilizer, increasing the potash concentration and decreasing the nitrogen yield. Importantly, while the method may stabilize large masses of ammonium nitrate by reducing phase changes in the ammonium nitrate, it is unclear what effect the potassium nitrate has on the detonation potential of the remaining ammonium nitrate if fuel oil were added.
Accordingly, it would be advantageous to provide a method for desensitizing or severely curtailing the explosive performance of fertilizers illicitly used in the manufacture of explosives. It would further be advantageous to provide a method which would have a minimal environmental impact when the product is used for its intended purpose as a fertilizer. An additive which imparts these properties must be undetectable or difficult to separate from the fertilizer, and able to withstand dessication, elevated temperatures, and pressure.
It is, therefore, an object of the present invention to provide a method for desensitizing the detonation potential of ANFO manufactured from fertilizer grade ammonium nitrate.
It is another object of the present invention to incorporate a desensitizing agent in fertilizer grade ammonium nitrate which is difficult to separate from the ammonium nitrate prills.
It is still further an object of the present invention to incorporate a desensitizing agent in fertilizer grade ammonium nitrate which is environmentally benign when the ammonium nitrate is released for its intended purpose as a fertilizer.
According to the present invention, the above-described and other objects are accomplished by adding an encapsulated suppressant to ammonium nitrate prills. The suppressant desensitizes the detonation potential of ANFO manufactured from the modified ammonium nitrate. Shock waves which pass through the ANFO in response to an initiating device cause the suppressant to be released, desensitizing the ANFO and reducing or entirely eliminating the explosive performance of the ANFO. The encapsulated suppressant is environmentally benign, and is sufficiently small that it can be incorporated into ammonium nitrate prills where it is not easily separated.